Uav ground penetrating radar array

ABSTRACT

A GPR system the implements a modified multistatic mode of operation is provided. The GPR is suitable for mounting on an unmanned aerial vehicle. The GPR system has radar transceivers. The GPR system transmits transmit signal serially via the transceivers. For each transceiver that transmits a transmit signal, the GPR system receives a return signal acquired by each transceiver except for a return signal for the transceiver that transmits the transmit signal. The GPR system outputs of matrix of return signals that includes a null value for the return signals of the transceivers that transmit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. Pat. Application No.16/779,339, filed on Jan. 31, 2020, which is hereby incorporated byreference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

The United States government has rights in this invention pursuant toContract No. DE-AC52-07NA27344 between the U.S. Department of Energy andLawrence Livermore National Security, LLC, for the operation of LawrenceLivermore National Laboratory.

BACKGROUND

Many scientific, engineering, medical, and other technologies seek toidentify the presence of an object within a medium. For example, sometechnologies detect the presence of buried landmines in a roadway or afield for military or humanitarian purposes. Such technologies may useultra-wideband ground-penetrating radar (“GPR”) antennas that aremounted on the front of a vehicle that travels on the roadway or acrossthe field. The antennas are directed into the ground with the soil beingthe medium and the top of the soil or pavement being the surface. GPRsystems can be used to detect not only metallic objects but alsonon-metallic objects whose dielectric properties are sufficientlydifferent from those of the soil. When a radar signal strikes asubsurface object, it is reflected back as a return signal to areceiver. Current GPR systems typically analyze the strength oramplitude of the return signals directly to identify the presence of theobject. Some GPR systems may, however, generate tomography images fromthe return signals. In the engineering field, GPR systems have beendesigned to generate spatial images of the interior of concretestructures such as bridges, dams, and containment vessels to assist inassessing the integrity of the structures. In such images, thesubsurface objects represented by such images tend to appear as distinctbright spots. In addition to referring to a foreign object that iswithin a medium, the term “object” also refers to any characteristic ofthe medium (e.g., crack in the medium and change in medium density) thatis to be detected.

The linear array (or more generally array) of a GPR systems may havedifferent modes of operation: monostatic, multi-monostatic, andmultistatic. In monostatic mode, the signal transmitted by a transmitteris received only by the receiver of that same transceiver. Inmulti-monostatic mode, the transceivers of a linear array operate in themonostatic mode in sequence. In multistatic mode, each transceivertransmits in sequence and all the transceiver collects that returnsignal. When in multistatic mode, the transceivers are in transmit modesequentially and for each transmitted signal, each switch to receivemode in parallel to receive a return signal. If the linear array has Ntransceivers, then N return signals in multi-monostatic mode and N²return signals in multistatic mode are collected.

The use of a GPR system with land-based vehicles can be problematic forseveral reasons. For example, a land-based vehicle may not be able todetect a buried landmine soon enough to prevent its detonation. Asanother example, a land-based vehicle may not navigate rough terrain(e.g., mountainous) to collect data. Also, a land-based vehicle may taketoo long to travel to area to be scanned. To overcome limitations ofsuch land-based vehicles, unmanned aerial vehicles (“UAVs”), alsoreferred to as unmanned aircraft systems (“UAS”) or drones, have beenemployed. Unfortunately, because of the size, weight, and powerrequirements for operating a GPR system, the UAVs with a GPR system needto be both powerful and large. Such UAVs tend to be very expensive,special-purpose UAVs. Commodity UAVs, which tend to be low-cost, light,and inexpensive, cannot carry such GPR systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that illustrates an MMA architecture adaptedto operating in a modified multistatic mode of operation.

FIG. 2 illustrates a matrix of return signals.

FIG. 3 illustrates operation of a pre-compensation system for cellularcommunications.

FIG. 4 is a flow diagram that illustrates the overall functionalprocessing of the controller of the MMA system in some embodiments.

FIG. 5 is a flow diagram that illustrates the processing of a transmitantenna controller and a receive antenna controller of the PC systemwhen the receive antenna controller generates the PC transmit signal insome embodiments.

FIG. 6 is a flow diagram that illustrates the processing of an antennacontroller that generates a PC transmit signal in some embodiments.

DETAILED DESCRIPTION

In some embodiment, a modified multistatic array (“MMA”) system providesan architecture for a GPR system that can be implemented with a size,weight (e.g., 3 kg), and power that is suitable to be carried by UAVsthat, for example, weighs only 10 kg. Current GPR systems that supportmultistatic mode include precise timing electronics to ensure that whena transceiver transmits a signal in transmit mode, the transceiver canbe switched to receive mode at a precise time that is long enough toprevent the return signal from being saturated by the transmitted signalbut that is short enough to capture the return signal. Such precisetiming electronics tends to be large, heavy, and consume a considerableamount of power. Moreover, the precise timing electronics of a GPRsystem that supports multistatic mode may need to be replicated for eachtransceiver, which further increases the size, weight, and powerrequirements.

The MMA system avoids the need for such precise timing electronics byoperating the array of transceivers in a “modified multistatic mode”.The modified multistatic mode allows a GPR system to transmit signalsvia the transceivers of a GPR array in sequence and collect returnsignals via each transceiver other than for the transceiver thattransmitted the transmit signal. For example, if a GPR array has eighttransceivers (i.e., 1-8), the MMA system transmits a transmit signal viatransceiver 1 and receives the return signals via transceivers 2-8. TheMMA system then transmits a transmit signal via transceiver 2 andreceives the return signals via transceivers 1 and 3-8. The MMA systemthen transmits a transmit signal via transceiver 3 and receives thereturn signals via transceivers 1-2 and 4-8. The MMA system thencontinues to transmit transmit signals via transceivers 4-8 in sequenceand receive return signals via transceivers other than the transmittingtransceiver. When complete, the MMA system has received 7 return signalsfor each transceiver, which can be represented by an 8x8 matrix withdiagonal elements containing a null value (e.g., a zero value or a valuethat is ignore in subsequent processing for a total 56 (i.e., 64-8)return signals. The matrix can then be employed to identify objectswithin the medium.

Because the return signals are not collected by the transceivers thattransmit, the MMA system does not require the precise timing electronicsneeded to support a multistatic mode of operation. As a result, thesize, weight, and power requirements needed to operate in the modifiedmultistatic mode is much less than needed to operate in multistaticmode. The MMA system can thus be deployed on a UAV that is much smaller,lighter, and cheaper than the UAVs needed to support multistatic mode.Moreover, any difference in accuracy of object detection using modifiedmultistatic mode and multistatic mode is small enough that the use ofmodified multistatic mode in many application environments producesresults that are substantially equivalent to results produced usingmultistatic mode. In addition, although the MMA system can be deployedin a GPR system with a separate transmit antenna and receive antenna foreach transceiver, the MMA system can also be deployed in a GPR systemwith a single antenna for each transceiver with a switch to controlwhether the antenna is in transmit or receive mode. The use of a singleantenna for each transceiver further reduces the size and weight of aGPR system.

In some embodiments, a pre-compensation (“PC”) system applies a PCtechnique to a transmit signal to generate a PC transmit signal thatresults in a desired return signal. For example, the desired returnsignal for a GPR system may be flat except for a peak corresponding to abounce from the surface of the ground. When the PC transmit signal istransmitted with no clutter below the surface, the return signal will beapproximately the desired return signal. When the PC transmit signal istransmitted with clutter below the surface, the return signal will havea peak for the surface and peaks corresponding to the clutter. By usinga PC transmit signal, the GPR system can better differentiate the returnsignals from the surface and the clutter-resulting in better objectdetection.

To generate a PC transmit signal, the PC system transmits a transmitsignal and collects a return signal given standard environmentalconditions. Standard environment conditions may be, for example, aroadway with no subsurface clutter. The return signal may be consideredto be a version of the transmit signal that is degraded by environmentalconditions such as noise and object reflections. The PC system thengenerates a transfer function that inputs the transmit signal andoutputs the return signal. For example, the PC system may employ Weinerfilter estimation techniques (e.g., Weiner deconvolution) to generatethe transfer function. After the transfer function is generated, the PCsystem may employ various techniques to identify a PC transmit signalthat would result in the desired return signal. For example, the PCsystem may repeatedly adjust a PC transmit signal, apply the transferfunction to the adjusted PC transmit signal to generate a return signal,and generate a similarity score indicating similarity between the returnsignal and the desired return signal. The PC system may generate theadjustments using a minimization technique to identify adjustments thatresult in the return signal converging on the desired return signal.When the similarity score exceeds a similarity threshold (e.g., thereturn signal converges on the desired return signal), the PC transmitsignal can be transmitted given standard environmental conditions, andthe return signal will be the approximately desired return signal.

A GPR system may employ an arbitrary waveform generator to generate thePC transmit signal. Once the PC system generates the PC transmit signal,the PC system can provide the PC transmit signal (e.g., signature of thesignal) to the arbitrary waveform generator to generate the PC transmitsignal for the GPR system.

The PC system may be embedded with the GPR system and implemented usinga processor, a field programmable gate array, an application-specificintegrated circuit, and so on. The PC system may regenerate PC transmitsignals in real-time, for example, as the GPR system encountersdifferent environmental conditions or periodically. In this way, the PCtransmit signal can be dynamically adapted to the current environmentalconditions.

The PC system may be used in systems other than GPR system such ascellular communication systems (e.g., 4G and 5G). When used in acellular communication system, a cell tower may use the PC system togenerate a PC transmit signal that is adapted to the environmentalconditions encountered when that cell tower transmits to another celltower. Initially, the PC system of the cell tower transmits a transmitsignal to the other cell tower. The other cell tower can then send tothe transmitting cell tower the receive signal that it received. The PCsystem at the cell tower can then generate the PC transmit signal fromthe transmit signal and the receive signal sent by the other cell tower.The cell tower can use the PC transmit signal in subsequentcommunications with the other cell tower. Alternatively, the other celltower upon receiving the receive signal, assuming it knows the transmitsignal, can employ the PC system to generate the PC transmit signal andsend the PC transmit signal to the cell tower for subsequent use by thatcell tower.

Although the MMA system and the PC system are described primarily in thecontext of a radar array with the same number of transmitters andreceivers (N-by-N), the systems may be employed with radar arrays thathave different number of transmitters and receivers (N-by-M). Forexample, a radar array may have 8 transceivers, but only twotransceivers may be enabled to transmit such as the first and the eighthtransceivers. When the first transceiver transmits, the transceiversother that the first transceiver (i.e., the second through the eighth)receive the return signal. Similarly, when the eighth transceivertransmits, the transceivers other than the eighth transceiver (i.e., thefirst through the seventh) receive the return signal. In such a case,the return signals may be represented by an N-by-M matrix with thereturn signal for the transceiver that transmits set to a null value. Inaddition, the MMA architecture described below can be reconfigured(e.g., by reprogramming the processor of the controller, reconfiguringan FPGA of the controller, or replacing the controller) to transmit onlyusing selected transceivers and to receive on one or more transceiversthat do not include the transmitting transceivers. In this way, theoperation of a radar array can be tailored as needed to achieve thedesired objective without the need to change the hardware of the radarsystem.

FIG. 1 is a block diagram that illustrates an MMA architecture adaptedto operating in a modified multistatic mode of operation. The MMAarchitecture includes a signal generator 101, an amplifier 102, anattenuator 103, a demultiplexer 104, switches 105.1-105.N, transceivers106.1-106.N, a controller 107, and an aggregator 108. The signalgenerator repeatedly generates a transmit signal to be transmitted bythe transceivers. The amplifier and attenuator are tunable to adjust thepower of the transmit signal. The demultiplexer inputs the transmitsignals from the signal generator and a transceiver selection signalfrom the controller and directs the transmit signal to the selectedtransceiver. Each switch inputs a transceiver mode signal from thecontroller indicating a transmit mode to transmit the transmit signal ora receive mode to receive a return signal via the connected transceiver.To implement a modified multistatic mode, the controller providestransceiver selection signals to the demultiplexer to select thetransceivers in sequence. For each selected transceiver, the controllerprovides a transmit mode signal to the selected transceiver and areceive mode signal to the other transceivers. Thus, for eachtransceiver that transmits, return signals are collected by the othertransceivers. The aggregator inputs the transceiver selection signalfrom the controller and collects the return signals received by thetransceivers other than the transceiver indicated by the transceiverselection signal. The MMA architecture may employ an equivalent-timesampling technique to collect the return signals. With such a technique,the signal generator may generate the same transmit signal a multitudeof times, sampling the waveform at different points until the entiretransmit waveform has been reconstructed. For example, a radar impulsewaveform could be approximated by 512 samples for each transceiver. Whenthe controller provides a transceiver selection signal to thedemultiplexer, the transmit signal is sent to and transmitted by theselected transceiver 512 times. The other transceivers receive anequivalent-time sample of that signal that, after 512 pulses completesthe desired waveform. The aggregator outputs the equivalent-time sampledreturn signals as an N-by-N matrix. The diagonal of the matrix containsnull values because the return signal received by a transceiver that istransmitting is not used when in the modified multistatic mode. When thematrix is processed to identify objects, the values of the diagonals maybe set to a value, for example, based on the return signals received byadjacent transceivers.

FIG. 2 illustrates a matrix of return signals. The matrix is 8-by-8representing an MMA architecture with 8 transceivers. The columnsrepresent transceivers when transmitting, and the rows representtransceivers when receiving. For example, when transceiver 1 istransmitting, the column for transceiver 1 includes a null value forthat transceiver and the return signal received by the othertransceivers. Techniques for processing a matrix of return signals aredescribed in U.S. Pat. No. 8,766,845 that was issued on Jul. 1, 2014, isentitled “Object Detection with a Multistatic Array using Singular ValueDecomposition,” and is assigned to Lawrence Livermore National Security,LLC, which is hereby incorporated by reference. As described above, theprocessing of such a matrix with null values provides acceptable objectdetection results in many applications.

FIG. 3 illustrates operation of a pre-compensation system for cellularcommunications. Antennas 301 and 302 are in communications range.Antenna 301 initiates communications with antenna 302. The controllerfor each antenna stores the signature of a calibration transmit signalTx to be transmitted by antenna 301. Initially, antenna 301 transmits311 the calibration transmit signal Tx that is received 311 by antenna302 as a calibration receive signal Rx. The calibration receive signalRx represents the calibration transmit signal degraded by environmentalconditions. The controller for antenna 302 then generates 312 a PCtransmit signal PCTx. The PC system may generate a PC transmit signal byfirst applying a Weiner filter estimation technique to the calibrationtransmit signal and the calibration receive signal to generate atransfer function. The PC system then identifies the PC transmit signalthat when input to the transfer function results in an output thatmatches the desired receive signal. Antenna 302 then transmits 313 thePC transmit signal to antenna 301. After receiving the PC transmitsignal, antenna 301 encodes 304 data using the PC transmit signal andtransmits 315 the encoded PC transmit signal (PCTx+data) to antenna 302.The received encoded PC transmit signal that is received by antenna 302is also degraded by environmental conditions such that the receivedencoded PC transmit signal is an approximation of the desired receivesignal encoded with the data (Tx+data). Antenna 302 can then decode theencoded data based on the signature of the desired receive signal.

FIG. 4 is a flow diagram that illustrates the overall functionalprocessing of the controller of the MMA system in some embodiments. Thecontroller 400 may be implemented using a processor, a fieldprogrammable gate array, application-specific integrated circuit,discrete logic and so on. The controller may receive a notification eachtime a series (e.g., 512) of transmit signals are generated fortransmission by a single transceiver. The controller may includehardware to send in parallel a transceiver selection signal to thedemultiplexer and aggregator, a transmit mode signal to the selectedtransceiver, and a receive mode signal to the other transceivers. In thefollowing, the sending of the transceiver selection signal and thetransmit/receive mode signals are described as being performed serially,but the controller may include logic to send the signals in parallel. Inblock 401, the controller selects the first transceiver i. In blocks402-410, the controller loops selecting the transceivers in sequence andsending transceiver selection signals to the demultiplexer andtransmit/receive mode signals to switches for the transceivers. Indecision block 402, if all the transceivers have already been selected,then the controller completes a round of transmitting the transmitsignals via each transceiver, else the controller continues at block403. In block 403, the controller sends a transceiver selection signalto the demultiplexer indicating the selected transceiver i. In blocks404, the component selects a switch j. In decision block 405, if all theswitches have already been selected for the selected transceiver i, thenthe controller continues at block 406, else the controller continues atblock 407. In block 406, the controller waits for a signal indicatingthat the transmission of the transmit signal for the selectedtransceiver has completed (e.g., sent 512 times by the signalgenerator). The controller then selects the next transceiver i and loopsto block 402 to process the newly selected transceiver. In decisionblock 407, if the selected switch is associated with the selectedtransceiver, then the controller continues at block 408, else thecontroller continues at block 409. In block 408, the controller sends atransmit mode signal to the selected switch and continues at block 410.In block 409, the controller sends a receive mode selection to theselected switch. In block 410, the controller selects the next switchand loops to block 405.

FIG. 5 is a flow diagram that illustrates the processing of a transmitantenna controller and a receive antenna controller of the PC systemwhen the receive antenna controller generates the PC transmit signal insome embodiments. A transmit antenna controller 510 sends a calibrationtransmit signal to a receive antenna 520, receives a PC transmit signalfrom the receive antenna, and subsequently transmits data encoded usingthe PC transmit signal. In block 511, the transmit antenna controllertransmits the calibration transmit signal to the receive antenna. Inblock 521, the receive antenna controller receives the correspondingcalibration receive signal representing a degraded calibration transmitsignal. In block 522, the receive antenna controller generates atransfer function by applying Weiner filter estimation to thecalibration transmit signal and the calibration receive signal. In block523, the receive antenna controller finds a PC transmit signal PCTx thatwhen input to the transfer function generates the desired receive signaldRx. In block 524, the receive antenna controller sends the PC transmitsignal to the transmit antenna. In block 512, the transmit antennacontroller receives the PC transmit signal. In block 513, the transmitantenna controller selects the next data to send to the receive antenna.In decision block 514, if all the data has already been selected, thenthe transmit antenna controller completes its sending of data, else thetransmit antenna controller continues at block 515. In block 515, thetransmit antenna controller generates an encoded PC transmit signal thatis encoded with the data. In block 516, the transmit antenna controltransmits the encoded PC transmit signal to the receive antenna and thenloops to block 513 to select the next data to send. In block 525, thereceive antenna controller receives the corresponding encoded PC receivesignal that has been degraded by environmental conditions. In block 526,the receive antenna controller decodes the data of the encoded PCreceive signal using the desired receive signal.

FIG. 6 is a flow diagram that illustrates the processing of an antennacontroller that generates a PC transmit signal in some embodiments. Theantenna controller 600 transmits a calibration transmit signal, receivesa corresponding calibration return signal, generates a PC transmitsignal based on the calibration transmit signal, the correspondingcalibration return signal, and a desired return signal. The transmitantenna controller subsequently uses the PC transmit signal fortransmissions. In block 601, the controller transmits a PC transmitsignal. In block 602, the controller receives the correspondingcalibration return signal. In block 603, the controller generates atransfer function based on the calibration transmit signal and thecalibration return signal. In block 604, the controller finds a PCtransmit signal that when input to the transfer function generates adesired return signal. If the antenna controller is deployed with anarray of transceivers (e.g., a GPR system), the antenna controller maygenerate a PC transmit signal for each transceiver. When a transceivertransmits a calibration transmit signal, a calibration return signal maybe received by each transceiver. The antenna controller can thendetermine a calibration return signal to use to generate the transferfunction by, for example, selecting one of the calibration returnsignals, taking an average of the calibration return signal, or applyinganother statistical technique to generate a calibration return signal.In blocks 605-606, the controller loops transmitting the PC transmitsignal and receiving a PC return signal. In block 605, the controllertransmits the PC transmit signal. In block 606, the controller receivesthe PC return signal and stores the PC return signal for imageprocessing using the desired return signal. The controller then loops toblock 605 to again transmit the PC transmit signal.

The processing of the described systems may be implemented byprogramming a computing device that includes a central processing unitand memory. The programs may be stored on computer-readable mediainclude computer-readable storage media and data transmission media. Thecomputer-readable storage media include memory and other storage devicesthat may have recorded upon or may be encoded with computer-executableinstructions or logic that implement the described systems. The datatransmission media is media for transmitting data using signals orcarrier waves (e.g., electromagnetism) via a wire or wirelessconnection. Various functions of the described systems may also beimplemented on devices using discrete logic or logic embedded as anapplication-specific integrated circuit. The matrices of return signalsmay be processed locally by the UAV to detect objects or transmitted toa computing device for remote detection of objects.

The following paragraphs describe various embodiments of aspects of theMMA and PC systems. An implementation of the systems may employ anycombination of the embodiments. The processing described below may beperformed by a computing device with a processor that executescomputer-executable instructions stored on a computer-readable storagemedium, discrete logic components, and so on that implements thesystems.

In some embodiments, a method performed by an electronics systemassociated with a first signal system having a radar antenna. The methodtransmits the method comprising: a calibration transmit signal via theradar antenna. The method receives a calibration receive signal that isdifferent from the calibration transmit signal based at least in part ondegradation of the calibration transmit signal as it travels from thefirst signal system to a destination. The method identifies a transferfunction that maps the calibration transmit signal to the calibrationreceive signal. The method identifies a pre-compensated transmit signalthat when input to the transfer function outputs a desired receivesignal. The method transmits the pre-compensated transmit signal so thata resulting pre-compensated receive signal will approximate the desiredreceive signal based on a degradation of the pre-compensated transmitsignal as it travels from the first signal system to a destination. Insome embodiments, the calibration receive signal is a reflection of thecalibration transmit signal. In some embodiments, the calibrationreceive signal represents multiple reflections of the calibrationtransmit signal from multiple reflection surfaces. In some embodiments,the calibration receive signal is further different from the calibrationtransmit signal based on degradation of the calibration transmit signalresulting from the reflection. In some embodiments, the calibrationreceive signal is further different from the calibration transmit signalbased on degradation of the calibration transmit signal as it travelsfrom the destination to the first signal system. In some embodiments,the calibration transmit signal is a ground penetrating radar signal. Insome embodiments, the calibration receive signal is received by a secondsignal system and then transmitted by the second signal system to thefirst signal system.

In some embodiments, a method performed by an electronics systemassociated with a first signal system having a radar antenna isprovided. The method receives, via the radar antenna from a secondsignal system, a calibration receive signal corresponding to acalibration transmit signal transmitted by the second signal system viaa radar antenna. The calibration receive signal is different from thecalibration transmit signal based at least in part on degradation of thecalibration transmit signal as it travels from the second signal systemto the first signal system. The method identifies a transfer functionthat maps the calibration transmit signal to the calibration receivesignal. The method identifies a pre-compensated transmit signal thatwhen input to the transfer function outputs a desired receive signal.The method transmits, via the radar antenna to the second signal system,the pre-compensated transmit signal so that the second signal system cantransmit the pre-compensated transmit signal via a radar antenna whereina pre-compensated receive signal received via the radar antenna of thefirst signal system approximates the desired receive signal based atleast in part on degradation of the pre-compensated transmit signal asit travels from the first signal system to the second signal system. Insome embodiments, the first signal system and the second signal systemare part of a cellular communications network.

In some embodiments, a first signal system interfacing with a radartransmitter and receiver pair. The first signal system includes acomponent that controls transmitting a first signal via the radartransmitter. The first signal system includes a component that controlsreceiving a second signal via the radar receiver, the second signalcorresponding to a degradation of the first signal during transmission.The first signal system includes a component that controls identifying atransfer function that maps the first signal to the second signal andidentifies a third signal when input to the transfer function outputs afourth signal. The first signal system includes a component thatcontrols transmitting the third signal via the transmitter so that thethird signal is received as an approximation of the fourth signal basedon degradation that is similar to the degradation of the first signal.In some embodiments, the transmitter and receiver pair is a transceiverwith a single antenna. In some embodiments, the transmitter and receiverpair includes a transmit antenna and a receive antenna. In someembodiments, the second signal is a reflection based on the firstsignal. In some embodiments, the first signal is a ground penetratingradar signal. In some embodiments, the second signal is received by asecond signal system and then transmitted by the second signal system tothe first signal system.

In some embodiments, a signal system for controlling an array oftransmitter and receiver pairs to operate in a modified multistatic modeis provided. The first signal system includes a controller that, foreach of the transmitter and receiver pairs in sequence, directs thetransmitter of that transmitter and receiver pair to transmit a transmitsignal and directs receivers of the other transmitter and receiver pairsto acquire a return signal from the transmit signal. The first signalsystem includes an aggregator that, for each of the transmit signalstransmitted by a transmitter, receives a return signal acquired by thereceivers. The aggregator further provides the acquired return signalswherein the provided acquired return signals do not include a returnsignal for each receiver when the transmitter paired with that receivertransmitted the transmit signal. In some embodiments, the transmitterand receiver pairs are transceivers and when a transmitter of atransceiver transmits a transmit signal, the receiver for thattransceiver is not directed to receive a return signal for thattransmitted signal. In some embodiments, the controller further directsthe receiver for the transmitter and receiver pair that transmits thetransmit signal to acquire a return signal and wherein the aggregatordoes not provide the return signals acquired by the receivers of thetransmitter and receiver pairs that transmit the transmit signal. Insome embodiments, the transmitter and receiver pairs include a separatetransmit antenna and receive antenna and wherein the aggregator receivesthe return signals of the receivers of the transmitter and receiverpairs that transmits the transmit signal and not provide those returnsignals. In some embodiments, the signal system includes a demultiplexerand, for each transmitter and receiver pair, a switch associated withthat transmitter and receiver pair. The demultiplexer inputs thetransmit signals and directs the transmit signal to a switch fortransmission by the transmitter of the transmitter and receiver pairassociated with that switch as directed by the controller. Each switchcontrols the associated transmitter and receiver pair to transmit orreceive as directed by the controller. In some embodiments, the signalsystem is a ground penetrating radar system. In some embodiments, thecontroller includes logic to direct the receivers in parallel. In someembodiments, the signal system does not include a demultiplexer and thesignal is sent to the switches in parallel. In some embodiments, thesignal system is mounted on an autonomous vehicle. In some embodiments,the signal system does not include precise timing electronics to switchan antenna of a transceiver that transmits a transmit signal to receivea return signal of that transmitted transmit signal.

In some embodiments, a method performed by a ground penetrating radarsystem mounted on an unmanned aerial vehicle. The ground penetratingradar system includes radar transceivers. The method transmits atransmit signal serially by each transceiver. For each transceiver thattransmits a transmit signal, the method receives a return signalacquired by each transceiver except for a return signal for thetransceiver that transmits the transmit signal. In some embodiments, thereturn signal is acquired by the transceiver that transmits thecorresponding transmit signal but is not used in subsequent processingof the return signals. In some embodiments, the ground penetrating radarsystem does not include precise timing electronics to switch an antennaof a transceiver that transmits a transmit signal to receive a returnsignal of that transmitted transmit signal.

In some embodiments, a system for controlling an array of transceivers,each transceiver associated with an antenna. The system includes ademultiplexer that, in response to a transceiver selection signalindicating a transceiver, directs an input to an output for thattransceiver. The system includes, for each of the transceivers, a switchthat in response to a transmit mode signal indicating to transmit,directs an input connected to the output of the demultiplexer for thattransceiver to a transmit output for the antenna of that transceiver,and in response to a receive mode signal indicating to receive, directsan input from the antenna of that transceiver to a receive output. Thesystem further includes a controller to, for each transceiver, send atransceiver selection signal for that transceiver to the demultiplexer,and send a transmit mode signal to the switch for that transceiver and,for transceivers other than that transceiver, send a receive mode signalto the switches for those transceivers. In some embodiments, the systemand the array of transceivers is mounted on an unmanned aerial vehicle.In some embodiments, the system further includes a signal generator togenerate the transmit signals that are input to the demultiplexer. Insome embodiments, the signal generator generates multiple transmitsignals for each transceiver and employs equivalent-time sampling of thesignals. In some embodiments, the system further includes an amplifierand attenuator for tuning the generated transmit signal prior to inputto the demultiplexer. In some embodiments, the system further includesan aggregator that receives the return signals and provides a matrix ofreturn signals with a return signal for each transceiver other than thetransceiver that transmits the corresponding transmits signal whereinthe return signal for the transceiver that transmits is set to a nullvalue.

From the foregoing, it will be appreciated that specific embodiments ofthe technology have been described herein for purposes of illustrationbut that various modifications may be made without deviating from thescope of the invention. For example, the MMA system and the PC systemmay be deployed in a variety of radar systems. For example, the systemmay deploy on various type of unmanned vehicles (“UVs”) such as UAVs,unmanned underwater vehicles (“UUVs”), unmanned space vehicles (“USVs”),and so on. For example, when deployed in a USV, the system may be usedto detect space junk. Accordingly, the invention is not limited exceptas by the appended claims.

1. A signal system for controlling an array of transmitter and receiverpairs to operate in a modified multistatic mode, the signal systemcomprising: a controller that, for each of the transmitter and receiverpairs in sequence, directs the transmitter of that transmitter andreceiver pair to transmit a transmit signal and directs receivers of theother transmitter and receiver pairs to acquire a return signal from thetransmit signal; and an aggregator that, for each of the transmitsignals transmitted by a transmitter, receives a return signal acquiredby the receivers; and provides the acquired return signals wherein theprovided acquired return signals do not include a return signal for eachreceiver when the transmitter paired with that receiver transmitted thetransmit signal.
 2. The signal system of claim 1 wherein the transmitterand receiver pairs are transceivers and when a transmitter of atransceiver transmits a transmit signal, the receiver for thattransceiver is not directed to receive a return signal for thattransmitted signal.
 3. The signal system of claim 1 wherein thecontroller further directs the receiver for the transmitter and receiverpair that transmits the transmit signal to acquire a return signal andwherein the aggregator does not provide the return signals acquired bythe receivers of the transmitter and receiver pairs that transmit thetransmit signal.
 4. The signal system of claim 1 wherein the transmitterand receiver pairs include a separate transmit antenna and receiveantenna and wherein the aggregator receives the return signals of thereceivers of the transmitter and receiver pairs that transmits thetransmit signal and not provide those return signals.
 5. The signalsystem of claim 1 wherein the signal system includes a demultiplexerand, for each transmitter and receiver pair, a switch associated withthat transmitter and receiver pair, wherein the demultiplexer inputs thetransmit signals and directs the transmit signal to a switch fortransmission by the transmitter of the transmitter and receiver pairassociated with that switch as directed by the controller, wherein eachswitch controls the associated transmitter and receiver pair to transmitor receive as directed by the controller.
 6. The signal system of claim1 wherein the signal system is a ground penetrating radar system.
 7. Thesignal system of claim 1 wherein the signal system is mounted on anautonomous vehicle.
 8. The signal system of claim 1 wherein the signalsystem does not include precise timing electronics to switch an antennaof a transceiver that transmits a transmit signal to receive a returnsignal of that transmitted transmit signal.
 9. A method performed by aground penetrating radar system mounted on an unmanned aerial vehicle,the ground penetrating radar system having radar transceivers, themethod comprising: transmitting a transmit signal serially by eachtransceiver; and for each transceiver that transmits a transmit signal,receiving a return signal acquired by each transceiver except for areturn signal for the transceiver that transmits the transmit signal.10. The method of claim 9 wherein the return signal is acquired by thetransceiver that transmits the corresponding transmit signal but is notused in subsequent processing of the return signals.
 11. The method ofclaim 9 wherein the ground penetrating radar system does not includeprecise timing electronics to switch an antenna of a transceiver thattransmits a transmit signal to receive a return signal of thattransmitted transmit signal.
 12. A system for controlling an array oftransceivers, each transceiver associated with an antenna, the systemcomprising: a demultiplexer that, in response to a transceiver selectionsignal indicating a transceiver, directs an input to an output for thattransceiver; for each of the transceivers, a switch that in response toa transmit mode signal indicating to transmit, directs an inputconnected to the output of the demultiplexer for that transceiver to atransmit output for the antenna of that transceiver, and in response toa receive mode signal indicating to receive, directs an input from theantenna of that transceiver to a receive output; and a controller to,for each transceiver, send a transceiver selection signal for thattransceiver to the demultiplexer, and send a transmit mode signal to theswitch for that transceiver and, for transceivers other than thattransceiver, send a receive mode signal to the switches for thosetransceivers.
 13. The system of claim 12 wherein the system and thearray of transceivers is mounted on an unmanned aerial vehicle.
 14. Thesystem of claim 12 further comprising a signal generator to generate thetransmit signals that are input to the demultiplexer.
 15. The system ofclaim 14 wherein the signal generator generates multiple transmitsignals for each transceiver and employs equivalent-time sampling of thetransmit signals.
 16. The system of claim 14 further comprising anamplifier and attenuator for tuning the generated transmit signal priorto input to the demultiplexer.
 17. The system of claim 12 furthercomprising an aggregator that receives the return signals and provides amatrix of return signals with a return signal for each transceiver otherthan the transceiver that transmits the corresponding transmits signal.